1. Field of the Invention
Aspects of the present invention relate to a color space conversion apparatus and a method of controlling the same, and more particularly, to a color space conversion apparatus performing gamut mapping in which an input color signal is properly converted such that color gamuts between a standard color signal of an input device and an output device reproducing the standard color signal are matched up to each other so as to improve color reproduction, in the case that the color gamuts differ from each other, and a method of controlling the same.
2. Description of the Related Art
In general, color reproducing devices (such as a monitor, a scanner, a printer, etc.) use different color spaces or color models according to respective fields of use. For example, a color image printing devices uses a cyan, magenta, and yellow (CMY) color space, and a color cathode ray tube (CRT) monitor or a computer graphic device uses a red, green, and blue (RGB) color space. Furthermore, in order to define colors to be correctly reproduced by any device, device independent colors, such as Commission Internationale de l'Eclairage (CIE) color spaces, are used. The CIE color spaces typically include a CIE L*a*b (Lab) color space, a CIE-XYZ (XYZ) color space, and a CIE L*u*v (hereinafter, referred to as ‘Luv’) color space.
In addition to the above color spaces, the color reproducing devices may use different color gamuts. While the color space is a method of defining a color (i.e., a method of indicating the relation of a color with other colors), the color gamut is a color reproducing range. Thus, in the case that a color gamut of an input color signal and a color gamut of a device to reproduce the input color signal differ from each other, gamut mapping is applied. Gamut mapping is a method in which the input color signal is properly converted such that the color gamuts match each other and color reproduction is improved. For example, when the color gamut of an input device is wider than the color gamut of an output device, the output device transforms a color that cannot be reproduced by the printer into a color that can be reproduced by the printer, and then outputs the color.
Gamut mapping between different color devices is generally performed by a method in which a color space of an input color signal is converted, and then lightness (L) and chroma are mapped so that hue is not converted. Specifically, the input color signal is converted from a device dependent color space (such as an RGB color space and a CMYK color space) to a device independent color space (such as a Lab color space, a XYZ color space, and a Luv color space), the device independent color space is converted into a LCH coordinate system indicating hue, lightness, and chroma, and then gamut mapping with respect to lightness and chroma is performed on a plane in which hue is regular.
In gamut mapping, a method in which chroma is mapped while maintaining lightness, and a method in which lightness and chroma are concurrently converted (i.e., a vector mapping method) are generally used. Moreover, other methods modified from the above methods may also be used.
However, the conventional methods cannot effectively express reproducible ranges of all colors. For example, in a color image treating method disclosed in U.S. Pat. No. 4,758,885, all input color signals are uniformly compressed, thus causing excessive color transformation beyond necessity.